Abstract
Biaxially oriented starch/polyvinyl alcohol (PVA) films were prepared by stretching starch/PVA blend precursor films that were fabricated by extrusion casting via a twinβscrew extruder. Investigations on crystallization, orientation morphology, and mechanical properties of extrusion cast and stretched starch/PVA films were carried out by using differential scanning calorimetry, scanning electron microscope, wide angle Xβray diffraction (WAXD), and tensile testing. The fresh extrusionβcast starch/PVA films, which were almost amorphous, can crystallize spontaneously when aged at room condition. A good compatibility between starch and PVA was obtained by extrusionβcasting technology. The wellβdeveloped molecular orientation, which did not occur along the machine direction during the extruding process, was observed in stretched film samples. Stretching unaged films can induce crystallization and the orientation of crystalline structures during stretching, resulting in the changes in diffraction peaks of WAXD patterns. The effect of stretch ratio and the orientation distribution in the plane of the film on mechanical properties of stretched films was studied, and the equal biaxially oriented films were found to exhibit inβplane isotropy. Β© 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008